Thermal control of a space satellite in orbit is usually accomplished by balancing the energy emitted by the satellite as infrared radiation against the energy dissipated by internal electrical (and other) sources plus energy absorbed from the environment. Due to changing conditions as the satellite orbits there is strong need for a simple thermal control surface operable with low electric power. Components of an electrochromic thin film structure operating in the mid-infrared (1 to 14 microns) have been demonstrated at the University of Nebraska. Preliminary data show a potential for switching of up to 70% of the emissivity in the mid-infrared. The purpose of the Phase I proposal is to test the feasibility of a electrochromically switchable large area thermal control surfaces over the spectral range 1 to 30 microns. This covers most of the Blackbody radiation spectrum of a spacecraft at a few degrees Celsius. The proposed work partners the materials preparation capability at the University of Nebraska with the extensive optical and thermal measurements experience and capability at the J. A. Woollam Co., Inc.. In Phase II we will build and test large area devices and transfer the deposition technology to a commercial optical coatings company. The benefits of this research and development when carried through Phases I, II and III will be operating commercially available spacecraft thermal infrared optical switches. These also have application in laser defense weapons systems and infrared optoelectronics.